1. Field of the Invention.
The present invention relates to mechanical joints and robot wrists, and in particular, it relates to robot wrists having a displacement capability throughout a hemispherical operating range.
2. Description of the Prior Art.
Interest in robotics and the use of robots in industrial applications has greatly increased in recent years. One area in which the use of robots has become important is the replacement of humans in tasks that involve manual work, such as welding, material handling, paint spraying, and assembly. Many of these tasks require working in cramped spaces or performing complex maneuvers. To perform such tasks, a robot arm or wrist should be able to rotationally move in a range similar to a human wrist and at a dwell time acceptable for the particular task involved.
One article reviewing the development of robot arms and wrists is entitled, "Robot Wrist Actuators," Robotics Age, November/December 1982, pp. 15-22, and was written by the applicant of the present application. In the article, several characteristics are described that make robot wrists attractive. One characteristic is that a mechanical arm or wrist can be safely used in areas where there is a danger of explosion if the wrist is driven by hydraulic actuators. However, there are several disadvantages with the prior art robot arms and wrists. Some of the disadvantages are also enumerated in the above-mentioned article and include large and bulky mechanical joints, slow dwell time in some rotational directions and low mechanical efficiency.
A number of well known universal joints are illustrated and described on pages 16 and 17 of the Pictorial Handbook of Technical Devices by Pete Grafstein and O. Schwarz, published by the Chemical Publishing Company, Inc. of N.Y., 1971. Although rotational motion can be transmitted through the universal joints illustrated on pages 16 and 17, the universal joints cannot be used in operations for transmitting pitch, yaw and roll motion to an implement or tool member.
A rotary actuator mechanism is described in the Higuchi et al U.S. Pat. No. 4,009,644. However, the rotary actuator of the Higuchi et al Patent is not very useful for the transmission of pitch, yaw and roll motion to a tool or implement member.
A number of robot joints are illustrated in the Vykukal U.S. Pat. No. 3,405,406 and the Vykukal et al U.S. Pat. No. 4,046,262. The Vykukal patents decribe hard-type space suits that permit the user inside the space suit to move around somewhat unrestricted.
The Bolner U.S. Pat. No. 3,912,172 describes a back-drivable, direct drive, hydraulically-actuated pitch and roll actuator.
The Rosheim U.S. Pat. Nos. 4,194,437 and 4,296,681, which were issued to the applicant of the present application, describe hydraulic servomechanisms which impart rotary movements to a device to be driven.
The Stackhouse U.S. Pat. No. 4,068,536 describes a remotely-driven, mechanical manipulator. The manipulator is controlled by three concentric drive shafts which terminate in a spherically-spaced wrist mechanism.
The Totsuka U.S. Pat. No. 3,739,923 and the Niitu et al U.S. Pat. No. 3,784,031 describe a manipulator arm having two parallel rotating drive shafts in a beveled gear system which translates the drive shaft's rotating motion to a bending pitch motion and rotary roll motion in a tool member.
A mechanical wrist is described in German Pat. No. 2,752,236 that includes three eletric motors, providing pitch, yaw, and roll, which are mounted on the outside of a housing with the inside of the housing being hollow. The wrist is used for holding welding tongs and the hollow inside housing permits electrical power lines to be fed through the wrist.
The Molaug U.S. Pat. No. 4,107,948 describes a flexible robot arm that is composed of a number of mutually connected rigid links being connected at one end to a drive means and at the other end to a tool member that is to be rotated. Another robot arm is illustrated in the Wells U.S. Pat. No. 3,631,737. The robot arm of the Wells patent includes a plurality of rigid tubular sections joined end-to-end by flexible joints to form an articulated arm. The rigid sections are manipulated by slender control cables which are attached to the respective sections and selectively extend and retract.